current serum-based calibrator and quality control products used for measuring lipid and lipoprotein levels have been plagued with difficulties in stabilizing these materials for long term dry storage, because of the tendency for .beta.-lipoproteins such as LDL and VLDL to denature and/or aggregate due to their large molecular size and hydrophobic nature. In some instances, clinical chemistry laboratories have resorted to preparing human lipid quality controls by pooling patient serum containing different lipoprotein concentrations for short term use and storage at 2.degree.-8.degree. C. Due to the time-consuming nature and hazards associated with handling blood serum from multiple human samples to prepare serum pools, commercially available lyophilized quality control materials gained wide acceptance.
Unfortunately, many of these human blood plasma-based lyophilized control materials suffer from matrix effects caused by denaturation and/or aggregation of their protein components, especially endogenous LDL and VLDL, which can cause interferences in clinical chemistry measurements due to matrix turbidity. In order to circumvent such problems, many lipid quality control materials are formulated using either an animal serum base (i.e., endogenous TC is predominantly HDL) supplemented with HDL to elevate TC, or human delipidated plasma supplemented with HDL. Hence, there is a need for quality control products that stabilize human cardiovascular marker proteins, especially LDL (clinical studies indicate that there is a strong correlation between increased serum LDL and the incidence of coronary heart disease), to enable its direct measurement and/or detection with reagents/devices employing a new generation of more sensitive and specific immunoseparation/immunochemical assay technologies (Rifai, N. et al., Clin. Chem. 38:150-160, 1992).